Process for transferring heat



United States Patent 3,237,683 PROCESS FOR TRANSFERRING HEAT Ernest F. Silversmith, Limestone Acres, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Dec. 30, 1960, Ser. No. 79,560

7 Claims. (Cl. 165-1) This invention relates to a process for transferring heat, particularly in equipment having surfaces composed predominantly of aluminum or magnesium, by means of nonaqueous liquid heat transfer media which are substantially non-corrosive to such surfaces.

The development of automotive engines made of lightweight metals such as aluminum, magnesium and their alloys has given rise to the problem of providing a satisfactory liquid coolant for suchengines. The aqueous coolants, presently used for ferrous metal engines, are unsatisfactory for use with light-weight metals, having a strong corrosive action on such metals. Aluminum, magnesium, and their alloys which contain at least 80% by weight of aluminum or magnesium, are known to be corroded by water and glycol. Aluminum and alunium alloys containing 12-13% of silicon are not corroded by water or alcohols at .a pH below 8, but a pH of 9 or higher is needed to protect iron and steel from corrosion, and aluminum and its alloys are considerably corroded at these higher pHs unless an inhibitor is added. Magnesium and its alloys are severely corroded by water, aqueous glycol, pure glycol, and l-butanol. Furthermore, aqueous coolants, base on ethylene glycol, gradually oxidize on continued use and form detrimental acidic products.

It is an object of this invention to provide heat transfer liquids which have excellent heat transfer characteristics and which are substantially non-corrosive to metal surfaces containing from about 80% to 100% by weight of aluminum or magnesium, as well as to the other metals of heat exchange systems. Another object is to provide a process for transferring heat in heat exchange systems, having metal surfaces containing from about 80% to 100% by weight of aluminum or magnesium, by circulating a substantially non-aqueous, substantially noncorrosive, heat transfer fluid in such system, particularly in the cooling systems of internal combustion engines made of such metals. A further object is to provide heat exchange systems, particularly automotive engines, having metal surfaces containing from about 80% to 100% by weight of aluminum or magnesium and containing a heat transfer fluid which is substantially non-corrosive to the metals of such systems. Other objects are to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accord with this invention which includes the process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of at least one normally liquid N,N- dialkyl alkenecarboxamide of the formula RCO-NR wherein R represents a member of the group consisting of hydrogen and straight-chain alkyl groups of 1 to 8 carbon atoms and each R represents a straight-chain alkyl group of 1 to 8 carbon atoms. This invention further includes heat exchange systems, including automotive engines and their cooling systems, having metal surfaces of the above character and containing as the heat transfer fluids or liquids Coolants, compounds of the above recited class.

It has been found that the normally liquid N,N-dialkyl alkanecarboxamides of this invention have excellent heat 3,237,683 Patented Mar. 1, 1966 transfer characteristics and excellent thermal properties, and are substantially non-corrosive to aluminum, magnesium and alloys containing at least about 80% by weight of such metals. Ordinarily, they will be used in closed systems, but because of their low volatility they can be used effectively in open systems at temperatures up to about C. below their boiling points without replacement of fluid caused by loss due to evaporation. The N,N-dialkyl alkanecarboxamides of the present invention also appear to be not objectionably corrosive to the other metals which may be encountered in heat exchange systems, such as the cooling systems of internal combustion engines. Furthermore, such N,N-dialkyl alkanecarboxamides are in general well known compounds and many of them are commercially available, whereby their use for the purposes of this invention is economically advantageous.

This invention is particularly applicable to heat exchange systems which are made wholly or in part of aluminum, magnesium, or alloys thereof which contain at least about by weight of aluminum or magnesium, and wherein surfaces of such metals come in contact with the heat transfer fluid. Usually, the other constituents of the aluminum alloys will be one or more of magnesium, manganese, zinc,.silicon, copper, nickel, iron and tin; and the other constituents of the magnesium alloys usually will be similar except that they normally will also contain aluminum as a constituent. Such alloys are commonly used as construction materials in industry and are becoming of increasing importance, especially in the construct-ion of the new aluminum and magnesium automotive engines. Representative commercial alloys (used in the Examples presented hereinafter) have the following composition in percent by weight:

This invention is particularly adapted to the cooling systems of automotive or internal combustion engines which are adapted to be cooled by liquid coolants and which include metal surfaces containing from about 80% to by weight of aluminum or magnesium in contact with the liquid coolant. It is also applicable to other heat exchange systems composed in whole or in part of such metals, where corrosion caused by aqueous fluids constitutes a serious problem, as in chemical reactors and other equipment where such metals have replaced ferrous metals and wherein the heat transfer fluid is used either for cooling or for mild heating.

The heat transfer fluids of this invention consist essentially of at least one normally liquid N,N-dialky1 alkanecarboxamide of the formula RCONR wherein R represents a member of the group consisting of hydrogen and straight-chain alkyl groups of 1 to 8 carbon atoms and each R represents a straight-chain alkyl group of 1 to 8 carbon atoms, and in which the alkyl groups represented by R and R may all be the same or different. By at least one is meant that the fluid may consist of one or a mixture of any two or more of such compounds. By normally liquid is meant that the compounds are liquid at normal room temperatures and atmospheric pressure. The N,N-dialkyl alkanecarboxamides may be anhydrous or substantially anhydrous, that is, they may contain up to about 2% by weight of water without seriously affecting their non-corrosive properties. The preferred N,Ndialkyl alkanecarboxamides are those in which R and R contain 1 to 4 carbon atoms and, particularly, the N,N-dialkyl formamides and the N,N-dialkylacetamides in which each alkyl group is a straightchain alkyl group of 1 to 4 carbon atoms, e.g., N,N- dimethylformamide, N,N-dimethylacetamide and N,N-diethylacetamide. Representative N,N-dialkyl alkanecarboxamides, together with their melting points and boiling points (when known) are listed below, wherein the term liq. means that the exact melting point is not given in the literature, but is known to be below room temperature, and the B.P.s in parentheses are extrapolated from pressures below atmospheric.

The effectiveness of liquids as heat transfer fluids may be demonstrated by their heat transfer coefiicients, as determined by the following equation derived by A. P. Colburn [Trans. Am. Inst. Chem. Eng., 29, 174 (1933)] for the heat transfer coefiicient, h, of a moving liquid:

a=proportionality constant C =specific heat k=thermal conductivity G=rate of flow IL=VlSCOSltY in centipoises D=hydraulic diameter If a G WD- is assumed to be constant for a given cooling system, lzD- /aG' 0.33 0.67 (which is equal to will be a measure of the relative abilities of various coolants to transfer heat. Calculations of for a representative amide and a reference liquid are tabulated below with appropriate references. The values of C k and u are for 160 F., the temperature of the A.S.T.M. glassware corrosion test for engine antifreezes (A.S.T.M. designation D1384-55T) wherever possible.

Op It. s Liquid mag um en cal./g., cal./sec. Centi- 0. cm., C. poises N ,N-Dimethylformamide e 0. 5 b 0. 000396 e 0. 542 5. 4 (by wt.) aqueous ethylene glycol. z 0.76 h 0. 000734 I 2.0 5.1

3 0.33 0.07 Values of for other aqueous glyeols are:

50% aqueous glycol 9. 4 70% aqueous glycol 6. 5

=Di Methyl Formamide, Antistall Additive, Petroleum Chemicals Division, E. I. du Pont de Nemours & Co. No temperature is given in this reference.

P. F. Pagarey, C. R. St, Clair and W. L. Sibbitt, Trans. Am. Soc. Mecl1.Eng., 78.1169 (1956).

Viseosities in centistokes were measured at and 210 R, and viscosity at 160 F. was determined by the A.S.T.M. slope method. The density needed to convert to centipoises was taken from J. W, Bruehl, Z. Phys. Chem, 22, 373 (1897). The density is given for 72 F. in this reference.

8 Extrapolated from the data of C T. Shields, Rafi-1g, Eng, 59, S80 (1951).

Interpolated from the data of O. K. Bates and G. Hazzard, Ind. and Eng. Chem, 37, 193 (1945).

It will be apparent that the N,N-dimethylformamide has excellent heat transfer properties, approaching that of the 80% aqueous ethylene glycol solution.

In order to more clearly illustrate this invention and the advantageous results to be obtained thereby the following examples are given, wherein mg./dm. means milligrams per square decimeter.

Example 1 The A.S.T.M. glassware corrosion test for engine antifreezes (A.S.T.M. designation: D1384-55T) was carried out with the following modifications. A closed glass container of approximately 200 ml. capacity was used. The liquid, N,N-dimethy1acetamide, was stirred continuously but was not aerated during the test. A coupon of aluminum alloy, A.S.T.M. No. Sl2A, 3.0 cm. x 0.32 cm. x 0.95 cm. with a 0.64 cm. hole, was used; no other metals were present. The container was immersed in a constant temperature bath at 160 F. for 360 hours. There was no visible corrosion and the metal gained 4 mg./dm.

Example 2 The procedure of Example 1 was used with the following modifications. An open container of 35 ml. capacity was used, the liquid was not stirred, and the container was heated at 171 F. for 360 hours. After the coupon of aluminum alloy (A.S.T.M. No. S12A) had been heated with 25 ml. of N,N-diethylacetamide and 0.5 ml. of water by this procedure, there was no visible corrosion and the weight loss was 8 mg./dm.

Example 3 The procedure of Example 1 was used with the following modifications. The container was of 100 ml. capacity, open to the air, and not provided with a stirrer. A coupon of magnesium alloy, A.S.T.M. No. AZ9l-A, 3.0 cm. x 0.32 cm. x 0.95 cm. with a 0.64 cm. hole, electrically connected to cadmium and steel (a spring clip of cadmium plated steel, with some of the cadmium filed away to expose the steel, was attached to the coupon), was heated with 90 ml. N,N-dimethylformamide and 1 ml. water at 160 F. for 333 hours. There was no visible corrosion and the weight loss of the coupon was 10 mg./ dm.

Example 4 Following the details of Example 2, a coupon of magnesium alloy (A.S.T.M. No. AZ91-A) was heated with 25 ml. of N,N-diethylacetamide and 0.5 ml. of water. There was a very small amount of visible corrosion and the metal lost mg./dm.

It will be understood that the preceding examples have been given for illustrative purposes solely and that this invention is not limited to the specific embodiments described therein. On the other hand, it will be readily apparent to those skilled in the art that, subject to the limitations set forth in the general description, other N,N-dialkyl alkanecarboxamides and mixtures of any two or more thereof can be substituted without departing from the spirit and scope of this invention.

From the preceding description, it will be apparent that this invention solves a serious problem in the industry wherein aluminum, magnesium and their alloys have been substituted for ferrous metals in heat exchange systems, particularly in liquid cooled internal combustion engines. Particularly, this invention provides for effective operation of such heat exchange system while eliminating the problems of serious corrosion heretofore encountered. Accordingly, it will be apparent that this invention constitutes a valuable advance in and contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of at least one normally liquid N,N-dialkyl alkanecarboxamide of the formula RCONR' wherein R represents a member of the group consisting of hydrogen and straightchain alkyl groups of 1 to 8 carbon atoms and each R represents a straight-chain alkyl group of 1 to 8 carbon atoms.

2. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group containing of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of at least one normally liquid N,N-dialkyl formamide in which each alkyl group is a straight-chain alkyl group of 1 to 4 carbon atoms.

3. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system, a heat transfer fluid which consists essentially of N,N-dimethylformamide.

4. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of at least one normally liquid N,N-dialkylacetamide in which each alkyl group is a straight-chain alkyl group of 1 to 4 carbon atoms.

5. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about to by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of N,N- dimethylacetamide.

6. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of N,N- diethylacetamide.

7. The process for transferring heat, by means of a circulating heat transfer fluid in a heat exchange system having metal surfaces containing from about 80% to 100% by weight of a metal of the group consisting of aluminum and magnesium in contact with said fluid, which comprises circulating in said heat exchange system a heat transfer fluid which consists essentially of at least one normally liquid N,N-dialkyl alkanecarboxamide of the formula RCONR wherein R represents a member of the group consisting of hydrogen and straightchain alkyl groups of 1 to 4 carbon atoms and each R represents a straight-chain alkyl group of 1 to 4 carbon atoms.

References Cited by the Examiner UNITED STATES PATENTS 1,632,994 6/1927 Burgess 257127 2,237,910 4/1941 Nallinger 2571.3 2,308,246 1/1943 Polin et al. 25277 2,743,297 4/1956 Husted et al 25277 3,048,620 8/1962 SpiVack 260-561 FOREIGN PATENTS 466,421 9/1950 Canada.

OTHER REFERENCES Chemical Abstracts, vol. 52, column 17639b (1958). The Condensed Chemical Dictionary, sixth edition (1961), p. 395.

ROBERT A. OLEARY, Primary Examiner.

HERBERT L. MARTIN, CHARLES SUKALO,

Examiners. 

1. THE PROCESS FOR TRANSFERRING HEAT, BY MEANS OF A CIRCULATING HEAT TRANSFER FLUID IN A HEAT EXCHANGE SYSTEM HAVING METAL SURFACES CONTAINING FROM ABOUT 80% TO 100% BY WEIGHT OF A METAL OF THE GROUP CONSISTING OF ALUMINUM AND MAGNESIUM IN CONTACT WITH SAID FLUID, WHICH COMPRISES CIRCULATING IN SAID EXCHANGE SYSTEM A HEAT TRANSFER WHICH CONSISTS ESSENTIALLY OF AT LEAST ONE NORMALLY LIQUID N,N-DIALKYL ALKANECARBOXAMIDE OF THE FORMULA R-CO-NR''2 WHEREIN R REPRESENTS A MEMBER OF THE GROUP CONSISTING OF HYDROGEN AND STRAIGHTCHAIN ALKYL GROUPS OF 1 TO 8 CARBON ATOMS AND EACH R'' REPRESENTS A STRAIGHT-CHAIN ALKYL GROUP OF 1 TO 8 CARBON ATOMS. 